Vitamin C, ascorbic acid, is
one of the most important vitamins found in citrus juices, including orange
juice. Testing for vitamin C levels in different forms of orange juice is
also a favorite science project for many students. Due to the limited available
references on vitamin C levels in citrus juices and how it degrades
over time, this web site will attempt to provide some information on
the subject to help students find additional references for their science
projects.

Often projects find that orange juices made from frozen
concentrated orange juice (FCOJ) have the highest vitamin C levels as compared
to freshly squeezed or not-from-concentrate (NFC) juices. This is probably
due to the fact that vitamin C degrades over time in fresh and NFC, but doesn't
degrade as much in FCOJ due to it being frozen until reconstitution. If one
is comparing a NFC product that has been stored for about 3 weeks versus
a newly reconstituted FCOJ, the FCOJ would almost certainly have a higher
vitamin C concentration. Also another thing to consider is if the FCOJ is
reconstituted to the same strength as fresh or NFC. If one doesn't add enough
water, then the vitamin C (and other compounds) would be more concentrated.
Another consideration is that the vitamin C content changes through the harvest
season and orange variety also plays a part. Since most FCOJ is blended to
a larger extent than some NFCs, it is entirely possible that the NFC is produced
from a variety/season that has a lower vitamin C content.

According to Nagy and Smoot,
temperature and storage time affects the percent of vitamin C content of orange
fruits and orange juice. Different varieties of oranges also have different
levels of vitamin C. The mid-season variety, Pineapple Orange had the highest
levels, followed by the main early-season variety, Hamlin Orange. The late-season
Valencia Orange had the lowest vitamin C content. Additionally, it was found
that the longer the Valencia Orange fruit stayed on the tree, the lower the
vitamin C level. (Additional details on these orange varieties can be found
from links in The
Story of Florida Orange Juice - From the Grove to Your Glass.) Nagy
and Smoot also found that in orange juice containers, vitamin C loss was
due to oxidation by a residual air layer trapped within the container during
processing. The loss was faster in the first 2 weeks and was more evident at
higher storage temperatures. Therefore, orange juice must be kept cool to prevent
vitamin C degradation as it is excellerated at high storage temperatures.

Maturity state and position on the tree: Vitamin
C decreases during the ripening process. Immature fruit has the highest levels.
The position on the tree also affects vitamin C levels. Since sunlight exposure
enhances vitamin C levels, fruit positioned on the outside of the tree and
on the south side have higher levels. Shaded inside fruit has the lowest.

Type of citrus fruit (species and variety):
Early maturing varieties have higher levels that late maturing types.
Early Hamlin and Navel fruits have more vitamin C than the late maturing
Valencia. Tangerines tend to have lower levels of vitamin C than oranges
due to its lower acid levels. Studies have found that the peel had the highest
levels of vitamin C followed by the pulp then the juice. Only 26% of vitamin
C of a citrus fruit can be found in the juice. The peel had 53% and the pulp
and rag had 21%.

Parameters used for processing into different products:
Frozen concentrated orange juice (FCOJ) and
reconstituted FCOJ almost always have higher levels of vitamin C and is above
the 100% US RDA values. This is most likely due to blending of early-season
fruit with late season fruit. Canned single strength orange juice will have
lower vitamin C levels due to heating during the canning process. NFC, Not
-From-Concentrate, will vary due to the varieties being processed.

Type of container: In cans, which are not used
very much today, it was found that enamel-lined cans had higher losses of
vitamin C than plain tin cans. This was due to residual oxygen and vitamin
C reacting with the tin. Glass packed orange juice provides poor retention
of vitamin C, losing 10% after 4 months of storage. Older cardboard cartons
lost up to 20%. (Today, most cartons have specially designed multi-layered
oxygen and light barriers to protect both loss of vitamin C, flavor, and
to enhance shelf-life.) FCOJ packed in foil-lined cardboard cans retained
greater than 90% of their vitamin C after 12 months at -20°C.

Handling and storage:
Oxygen is the most destructive ingredient in
juice causing degradation of vitamin C. However, one of the major sugars
found in orange juice, fructose, can also cause vitamin C breakdown. The
higher the fructose content, the greater the loss of vitamin C. Conversely,
higher acid levels of citric and malic acids stabilize vitamin C. Orange
juice must be stored at proper cool temperatures with oxygen barriers for
best retention of vitamin C levels. When fresh citrus is stored at 38°F
for 12 weeks, there was no loss of vitamin C, but when stored at high
temperatures, the loss was great.

The
Orange Book-
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New book! - The Orange Book
follows the complete journey of orange juice. A must have book for the processor
and grower who wants to know everything possible about The
Orange!

Much of the information
on this page came from these references which you can look up at your local
University Library: